Nairobi, Kenya — Chosen with the overwhelming support of clan elders in January and thought to be Somalia's best hope for stability and peace, the government of Sheikh Sharif Ahmed now appears to be engaged in a fight for survival.

An unrelenting military assault by militant Islamist forces – coming just days after an international donors conference in Brussels promised some $213 million in direct aid to Mr. Sharif's moderate government – has chased Sharif's forces into retreat. The fighting has killed more than 150 since May 7 and has forced tens of thousands to flee their homes.

Whether the Sharif government stands or falls, or simply fails to expand its authority beyond the few dozen city blocks of Mogadishu currently under its control, the fighting is going to have its greatest effect on the Somali civilians who had just begun to return to their country after 19 years of war.

"Given the fact that there [are already] catastrophic living conditions in Somalia, with a drought in the country ... this only makes matters worse," says Andrea Pattison, spokeswoman for Oxfam in Nairobi, Kenya. "1.3 million people are already displaced in Somalia, and now you have reports of tens of thousands more fleeing their homes. It's a pretty dire situation."

The hard-line Islamist group Al Shabab says it rejects the Sharif government, despite the fact that Sharif won overwhelming support from Somali clans and traditional leaders during a United Nations-sponsored election held in Djibouti on Jan. 31.

Sharif, a former commander of the Union of Islamic Courts (UIC), was thought to have the credentials that would most appeal to Islamists – giving him the best chance of buying Somalia enough time to restore peace, open up humanitarian corridors for aid delivery, and allow for peaceful elections at a later time.

Sharif was applauded both for reaching out to fellow Islamists – and having parliament make Islamic law the basis for Somalia's legal system – as well as to Western donor nations eager to see Somalia's nearly 19 years of anarchy brought to an end.

Sharif even welcomed back the influential Sheikh Dahir Aweys, the former head of the UIC, hoping the two could resolve their differences by negotiation.

That appears to have failed.

Indeed, it is Mr. Aweys's return to Mogadishu that seems to have precipitated the most recent spate of fighting.

In a recent speech to supporters, Aweys reportedly lashed out against African Union peacekeepers in Somalia and against Sharif.

"The big upsurge in fighting came when Aweys came back to Mogadishu," says Roger Middleton, an expert on Somali politics at Chatham House, a think tank in London. "The optimistic thinking was that he'll come back, talk, and together with Sharif form a very broad power-sharing government. There doesn't seem to be any evidence of that working."

In a speech earlier this month, Sharif still held out hope for negotiating with Al Shabab. "We tell the Somali people that the government is making efforts to stop the fighting and work for the interest of the people, but, unfortunately, people who have made a career of war and do not want a government are wreaking havoc in the country," Sharif told reporters.

Hours after that speech, the presidential palace was shelled.

"The fighting is deeply unpopular with the people, and Al Shabab knows that and [Aweys] knows that, so they want to make a quick offensive, which they hope will overthrow Sharif," says Rashid Abdi, an expert on Somalia for the International Crisis Group in Nairobi.

But if this becomes a long stalemate, it will not work well politically for Al Shabab, he adds. "The Islamist movement is deeply fragmented, and there is a possibility of ... a fratricidal war between Islamists."